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COATINGSPRO SEPTEMBER 2016 67 FA air barriers require substrates that are struc turally suppor ted, smooth and continuous, dr y, clean and free of debris, and uninterrupted at transitions. Impacts of Air Leakage A lthough the requirements for air barriers have increased, there is still a lack of understanding as to the need for a properly designed and installed air barrier. If an air barrier is not installed to meet the principles noted earlier, it may allow air infiltration into the building, causing deterioration, such as ice dams, rot of wood walls and substrates, or corrosion of metal components. Unfortunately, many installed air barriers fail after a short period of time. ese failures are typically caused by a lack of understanding of how moisture intrusion works; failure to perform building modeling, review, or testing; a breakdown in coordi- nation between construction trades and details; a lack of defined expec- tations for a building's performance with regard to the air barriers; and poor workmanship. Advantages and Disadvantages Like most materials, FA air barriers have both advantages and disadvan- tages. First of all, FA air barriers are applied primarily via spray or roller. Material and equipment costs accrued during application usually exceed the costs associated w ith SA air barrier installation. However, the time and labor saved installing FA air barriers ty pically offset those costs, since substrate primers are not ty pically required for FA materials as they are w ith SA air barriers. A lso, a smaller crew can usually be used to apply FA air barriers. Once installed, FA air barriers are monolithic, while SA air barri- ers require field seams. Unlike the manufactured thickness of SA air barri- ers, though, FA air barriers accuracy is dependent on the installer and application methodology. It is up to the installer to achieve the correct thick- nesses and the associated performance characteristics that result. Exposure limits for FA materials are usually 60 to 90 days, sometimes less, depending on both the building elevation and material 's exposure to direct sunlight. If an FA air barrier is exposed longer than the manufactur- er's recommended allowable limits, "alligatoring" (aka cracking ) can occur. If the insulation and exterior cladding can't be installed until later, tempo- rar y protection needs to be applied over the air barrier. FA air barriers need to be properly stored prior to and after delivery to a jobsite. ese materials typically require storage away from precipitation and direct sunlight. Manufacturers provide minimum and maximum temperature limitation for the storage of their products, which is typically from 40° F to 100° F (4.4–37.8° C). Improper storage of the materials could negatively impact the application of the air barrier material. Meaning of Installation FA air barriers require substrates that are structurally supported, smooth and continuous, dry, clean and free of debris, and uninterrupted at transi- tions. In addition, the weather must be taken into account. e substrates need to be applied within the manufacturer's recommended temperature range and must not exceed allowable moisture content limitations prior to application. Additionally, manufacturers typically do not recommend applying FA material to a substrate within 24 hours of inclement weather. Each FA has a different composi- tion that will impact its installation and performance. For instance, The county courthouse building was to receive rigid insulation over the FA membrane. The roof assembly had not been installed prior to the FA air barrier installation. Peeling Air Barrier